<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title></title>
</head>
<body>

<script type="text/javascript">

let cast1 = new BroadcastChannel('mychannel');
cast1.onmessage = function (e) {
    alert(e)
};
</script>

    
</body>
</html>